The presence of extremely high healthcare expenditures per capita, including for elderly persons, is a major clinical, public health, and public policy problem in the U.S. The lack of efficiency in U.S. healthcare is directly related to extensive overuse of discretionary services as well as to substantial underuse of effective non-discretionary services. If personality is associated with healthcare use and expenditures in later life, then it could be a critical factor in the development of targeted and tailored interventions to address over- and underuse. However, it is not known whether personality is associated with healthcare expenditures. This study will establish whether this relationship exists. If the relationship exists, the long-term objective of this resubmitted R03 secondary analysis will be a program of research to develop interventions that take advantage of personality domains to address overuse and underuse among Medicare beneficiaries. An extensive literature shows that health status, beliefs, attitudes, and behaviors and healthcare decision-making are all related to personality. There is strong consensus that the major dimensions of human personality can be grouped into 5 broad domains known as the "Big Five": Neuroticism, Extraversion, Openness to Experience, Agreeableness, and Conscientiousness. The Big Five will be assessed using the NEO-Five Factor Inventory (NEO-FFI). While 9 studies have found an association between personality domains and health services use, only one included exclusively persons age 65 and older, and 5 of the 9 focused on mental health services. The Specific Aims are to establish if associations exist between personality domains and (1) Medicare, non-Medicare, and total healthcare expenditures, (2) 4 of the most expensive acute and long term care services (acute hospital days, emergency department visits, nursing home days, and custodial home care hours), and (3) high versus low discretionary healthcare services. The data were collected from 1308 community-dwelling Medicare beneficiaries participating in the Medicare Primary and Consumer-Directed Care Demonstration. A large part of the study's significance derives from the sample, which is made up of groups (lower SES/education) that rarely participate in intensive research. Outcome variables are expenditures calculated from utilization data collected via daily Health Care Journals for 30 healthcare services (Aim 1), categories of utilization obtained from these daily Journals (Aim 2), and Medicare claims data provided by the Centers for Medicare and Medicaid Services (Aim 3). Utilization will be estimated by negative binomial, two- part, and/or hurdle regression models. Two-part generalized linear models will be employed for expenditures. Standard errors and 95% confidence intervals will be estimated using clustered non-parametric bootstrap methods. The establishment of associations between personality and healthcare use or expenditures will lead to studies designed to establish causal mechanisms and ultimately to interventions that are targeted or tailored to characteristics of individuals that overuse discretionary or underuse effective non-discretionary services. PUBLIC HEALTH RELEVANCE: The proposed study is highly relevant to public health because overuse of some discretionary healthcare services and underuse of effective, readily available, non-discretionary services represent major public policy problems and potential threats to public health, especially for Medicare beneficiaries. The public health and policy implications of the relationship between personality and healthcare use and expenditures in later life have rarely, if ever, been considered. If we are able to show associations between personality domains and healthcare use and expenditures, we anticipate convening a conference to explore the clinical, public health, and policy implications of the role of personality for healthcare services utilization and expenditures in order to be able to develop clinical trials to investigate targeted and tailored interventions and community-based translational effectiveness studies to reduce overuse of discretionary healthcare services and increase underuse of effective non-discretionary services.